Inorganic semiconducting materials, for example semiconducting metal oxides, have found widespread use in the electronic industry, for example in thin film transistors (TFTs). To obtain semiconducting layers of acceptable charge mobility it has proven advantageous to deposit the inorganic semiconducting materials onto a supporting layer by means of vapor gas phase deposition methods. These methods, however, require high vacuum and frequently also necessitate a thermal post-treatment to further improve the charge mobility of the semiconducting layer.
Without wishing to be bound by theory it may be that the limited charge mobility directly following deposition is due to the particulate nature of the inorganic semiconducting materials. Charges are quickly transported within a particle of the inorganic semiconducting material but are slowed down when having to “jump” from one particle to the next. It is believed that thermal post-treatment (or “sintering”) increases the particle sizes and therefore decreases the number of interfaces between particles.
However, gas phase deposition methods are not well suited for industrial production of large area coatings. For mass production, industry is therefore turning to other deposition methods, such as for example various printing methods as for example ink-jet printing. For inorganic semiconducting materials their limited solubility has proven to be a major drawback, which may potentially be avoided for example by applying a soluble inorganic precursor, for example a soluble metal complex, which is then converted into the respective semiconducting compound, or by applying a metal compound particle dispersion. In either method the applied layer, either of the soluble inorganic precursor or the metal compound particle dispersion, needs to be heated, so as to convert the precursor into the semiconductor compound and sinter the particles. The precursor conversion generally requires temperatures of around 300° C., thus rendering this method unsuitable to be used with many polymeric substrates, which are of interest particularly for flexible and/or light-weight electronic devices.
Examples of soluble inorganic precursors are zinc acetate, as for example disclosed in B. Sun et al., J. Phys. Chem. C, 2007, 111, 18831-18835, and zinc oximates as for example disclosed in WO 2012/000594 A1. As discussed in B. Sun et al., J. Phys. Chem. C, 2007, 111, 18831-18835 these precursors require heating to at least 250° C. in order to convert them into the inorganic semiconductor material and to remove any organic residues as well.
An example of a composition comprising zinc oxide nanoparticles and perylene di-imides is disclosed in S. Bubel et al., Physica E 44 (2012) 2124-2127. However, the resulting transistors were characterized by very low charge carrier mobility of 7.5·10−5 cm2 V−1 s−1 and an Ion/Ioff ratio of 103.
Consequently there is a need for a composition and/or a process that would avoid the drawbacks of the existing compositions and processes and would particularly allow to work at lower temperatures than in known methods.
It is therefore an object of the present application to provide a semiconductor composition and/or a process allowing the production of a semiconducting layer at reduced temperatures.
It is also an object of the present application to provide a semiconductor composition and/or a process allowing the production of a semiconducting layer having good semiconducting properties.
It is a further object of the present application to provide a semiconductor composition and/or a process allowing simplified production of electronic devices.
Additional objects of the present application become evident from the following description as well as the examples.